perf(connect): lazy-load onboarding intro images

The agent introduction slides forced eager loading via `priority`, so the
large Connect PNGs were preloaded up front, slowing the "Select agent" step.
Switch to loading="lazy" and compress the Connect intro assets.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: Tanya-atatakai

frontend/components/AgentIntroduction/IntroductionStep.tsx

@@ -41,7 +41,7 @@ const AnimatedImage = ({ imgSrc, alt, imageHeight }: AnimatedImageProps) => (
       <Image
         src={imgSrc}
         alt={alt}
-        priority
+        loading="lazy"
         width={0}
         height={0}
         sizes="100vw"